As is well known by the public and particularly those in the petroleum and automotive industries, the forces limiting supplies and increasing prices of liquid hydrocarbon fuels have provided the impetus for the development of better and more efficient engines. The factors sought in general are low first cost, low maintenance costs, long service life, low vibration and noise, good fuel economy, low emissions, low bulk and weight, fast response, easy starting, and ability to utilize a wide range of hydrocarbon fractions.
Desirable properties for most efficient use of the fuels include combustion at the highest possible temperature, a short fuel burning time, completeness of combustion before expansion, low radiation, conductive and convective heat loss to the confining structure. Low exhaust gas temperature following the maximum extraction of mechanical work during the expansion process is a cycle design food for high efficiency. Mechanical considerations for most efficient use of the materials of construction include high strength/density ratio for the minimum material cost, the least possible use of exotic or rare alloying elements, high internal damping coefficient for parts subject to vibration, and long fatigue/wear life for parts which move or which are subject to flexure and/or abrasion.
Conventional two-cycle or four-cycle reciprocating or rotary engines utilize intermittent or cyclic combustion processes to permit in turn a lower average temperature suitable to the materials such as aluminum or cast iron. The combustion temperatures exceed 3,000 degrees F. for a short time, but the average piston temperature is lower than 500 degrees F. as heat is conducted away by coolants, lubricants, and the incoming charge air.
Gas turbine engines employ constant pressure combustion and continuous burning within a combustion chamber supplied with excess air for cooling the chamber walls and protection of the turbine nozzle and blading. Extremely high speeds of rotating compressors and turbines pose a potential hazard and require protective shields in the plane of rotation. The main advantages are very light weight, complete combustion, and freedom from vibration. The disadvantages of turbines include slow starting, high fuel consumption particularly at part power operation, susceptibility to blade erosion and damage which results in degraded performance, and sensitivity to matching compressor flow to the turbine capacity without stalling or surging the flow in the compressor.
The engine industry has attempted to combine the multi-piston reciprocating engine with high speed turbines in combiantions ranging in form from turbinecharged engines that have been commonly accepted for over 40 years, to free-piston engines that have been used as the combustor for power turbine output drives. All of these attempts have sought to use the highly efficient but momentary and cyclic operation of the piston-cylinder combustion chamber.
In any open cycle heat engine the working fluid experiences three major processes, namely compression, heating and expansion. Each of the three major processes may be carried out in a separate component and thus one separates the various processes. By contrast, heat engines like the Otto and Diesel cycles are designed as a single physical component to carry out the required functions which occur at successive times. Thus such engines are intermittent combustion engines.
If the designer can develop each component to deal with its particular function and characteristic without being involved with the other two functions, then the efficiency of each process can be increased significantly. For example, the compressor component can be designed without considering high temperature, emission characteristics, etc. since its only function is to compress and deliver air to the combustion component. Ideally, the combustor's single purpose is to receive the compressed air from the compressor and to receive fuel which is separately introduced. The separation of components allows continuous combustion and therefore the combustion process has a truly multi-fuel capability limited only by the designer's ability to inject the fuel into the combustion chamber. Gaseous, solid or liquid fuels could be used in this steady, constant pressure combustion process.
This invention improves the efficiencies of a predecessor engine as shown in U.S. Pat. No. 4,336,686 by using crank shafts instead of a cam configuration. The instant invention departs radically from the engine in the referenced patent because of the positive connection through the cranks to convert reciprocal to rotary motion. Thus, the prior patent is not pertinent to the engine described and claimed herein. Applicant knows of no art which is pertinent to this invention.